In ground control systems, such as mine roof, retaining wall and rock wall support systems (hereinafter collectively generally referred to as “mine roof support systems”), threaded rod-like reinforcing bolts, rebars, tendons or anchor rods are embedded into 1 to 2.5 inch diameter bore holes which are drilled into the rock complex. The rebar, bolt or anchor rods are secured in place within the bore hole by a resin or grout. Typically, the resin used to secure the reinforcing rods consists of a two-part resin which is provided in frangible cartridges sized for insertion into the bore hole immediately ahead of the rod or is pumped prior or after the bolt is installed.
Depending on the ground support type used, the reinforcing rods or bolts each vary from 2 to 30 feet in length and are made of steel and provided with a threaded outermost proximal end for installing a nut or other torquing mechanism. Other bolts may use a forged type head for installing the bolt. The thread nut and/or forged head may be used to secure a washer plate. Other bolts such as cable bolts may use a barrel and wedge type devise to apply load to the roof or wall. The bolts are positioned in the bore hole so that the threaded end projects outwardly beyond the rock face, allowing the threaded coupling of a nut thereto.
Frequently, a torquing mechanism will consist of either a dome nut, pin nut or any other torquing mechanism such as the “buddy nut”, and used to rotate the bolt, to assist in the mixing of resin or grout compositions. The domed nut end cover is formed with a thickness selected so that its initial engagement with the threaded end tip of the bolt prevents further movement of the nut onto the bolt end under initial torque forces. The pin nut is installed on the bar and is secured via a roll pin or any other type of pin. The buddy nut is a nut that has a plastic cap inserted into the end of the nut that is installed through on hole the nut preventing the nut from further movement onto the threaded section. Other nut types or methods of spinning and/or torquing the bars may exist. This therefore allows the bolt to rotate together with the turning of the nut. As the resin sets, resistance to the rotation of the bolt increases to a point where the rotational forces applied to the nut, exceed a critical minimum or threshold force whereby the dome end splits or deforms, allowing the nut to be tightened along the bolt and against the rock face. Following the setting of the resin, the threaded fastener is run along to the projecting end of the bolt and tightened against the rock face to consolidate rock forces, and control ground movement. Applying a torque isn't always necessary; therefore other methods of securing a plate may be used such as a forged head or in the case of a cable bolt, a barrel and wedge cable grip or other means of securing a plate can be used.
International publication No. WO 02/02910 A2 to Gauderau, published Jan. 10, 2002 describes a yieldable cone bolt construction used as a reinforcing rod in mine roof support systems. The cone bolt described in Gauderau consists of a steel bar which has a conical wedge-shaped projection at its inner, distal-most end. The cone shape projection extends radially outwardly in a direction away from the proximal end of the bolt to a preferred maximum diameter of about 2.5 cm. A 2 to 2.5 cm long mixing tab is mounted to the end of the conical projection. The tab assists in the mixing of resins in the initial placement of the cone bolt as it is rotated. The cone bolt is constructed so that it may pullout or “yield”, sliding axially in the bore hole, to effect ground control. In particular, in the event of shock or load, the cone bolt acts to counter ground forces by limited yielding, with a desired pullout strength, moving axially outwardly so as to pull the frustoconical wedge through the harden resin and dissipate ground forces.
In the installation of yieldable mine roof support systems, it is therefore desirable to minimize any chemical adhesion between the resin and the cone bolt, which would otherwise interfere with yielding movement of the bolt. In particular, if the bolt is unable to yield, the bolt may otherwise fracture and fail completely. To minimize such adhesive contact, cone bolts are typically packaged and shipped in crates coated with grease. Immediately prior to installation, the installer uses a rag to wipe any excess grease from the surface of the cone bolt prior to its positioning within the bore hole
The applicant has appreciated various disadvantages exist with the installation and use of conventional cone bolts. The packaging of cone bolts in crates immersed in grease, and the requirement to manually remove excess lubricant is both unpleasant to the installer and results in the increased possibility of contamination of both the environment and other equipment by the lubricant. This furthermore increases the chance that the bolt and/or the bolt installation tool could slip from the installer's hands, leading to damage or injury.
In addition, the application of heavy grease coatings increases the possibility that dust, dirt and other debris typically present in mining environments could adhere to the bolt prior to its insertion. Such debris may adversely contaminate the resin compositions, decreasing its effectiveness.
Furthermore, the requirement to manually removing excess lubricant from the surface of the bolt and the rotation of the bolt during resin mixing frequently produces variations in the thickness of the lubricant coating. Analytical testing has suggested that the rotation of the bolt by itself within unset resin, frequently results in the lubricating grease being stripped entirely from the bolt surface, resulting in chemical bonding between the resin and the bolt, which could interfere with yielding movement.